To form a cooperative group of Radiation Therapy Research and Clinical Centers for the purpose of conducting joint clinical investigations. This group will undertake clinical trials and other cooperative studies in an endeavor to advance knowledge in the curative and palliative management of cancer. Through the collaboration of the radiotherapy centers joined in the Radiation Therapy Oncology Group, it will be possible to provide an adequate number of patients to answer significant questions in the treatment of cancer, not possible on the basis of the number of patients seen in any one institution. A sophisticated biostatistical center, as an integral part of the Radiation Therapy Oncology Group, will ensure satisfactory methodology of the studies, and aid in establishing an order of priorities for those studies which are of the greatest, immediate importance and which can yield an answer in a reasonable period of time. This group will make possible the collection of long-term data with regard to radiation complications as well as patient survival; the group will integrate study programs in cancer with those in other disciplines and enrich training programs in oncology and radiation therapy.